Manœuvres to avoid collision

Abstract

The Rules given in this chapter require power-driven vessels in sight of one another when in a meeting situation to turn to starboard and, when in a crossing situation, to avoid crossing ahead of a vessel on the starboard side, and to avoid turning to port for a vessel on the port side. For vessels not in sight of one another, rule requires that alterations of course to avoid a close quarters situation should not be to port for a vessel forward of the beam and should not be towards a vessel abeam or abaft the beam. Rules effectively require that alterations of course should normally be to starboard for a vessel forward of the beam and on the port quarter and to port for a vessel on the starboard quarter. However, no guidance is given in the Rules as to the magnitude of such alterations, apart from the requirement that they should be substantial and large enough to be readily apparent to another vessel observing visually or by radar. If each of the two vessels, approaching to involve risk of collision in a meeting or crossing situation, detects the other forward of the beam and alters course to starboard the action of one vessel will usually complement the action of the other. Each vessel would be taking action, which would cause the line of sight to rotate in an anticlockwise direction, i.e., cause the compass bearing to decrease. However, the effectiveness of helm action will obviously not continue to increase indefinitely with the angle through which the vessel turns. There will always be an optimum value beyond which the effect on the nearest approach will be reduced. An alteration to starboard equal to twice the angle between the bearing of the other ship and the port beam will have no effect on the distance of the nearest approach.